1. Field of the Invention
The present invention relates to a lamination method for a transparent substrate, and in particular to a method for forming a single-crystal silicon layer on a transparent substrate.
2. Description of the Related Art
In addition to developing flat panel displays with greater display areas, the lighter, thinner, and more flexible characteristics of flat panel displays have also become desirable. One current trend is to substitute glass substrates with plastic substrates. However, many problems, such as low Tg, arise when using plastic substrates, which hinder the required high temperature process, resulting in poor panel performance. Moreover, plastic substrates are poorly suited to the manufacturing process, which induces severe stress, static and large thermal expansion coefficient. Other alternative substrate materials include metal, or metal alloy, such as aluminum, titanium or similar. Use of these substrate materials have the advantages of light weight, flexibility, high melting point, no static, lower thermal expansion coefficient, and lower cost. Therefore, these materials demonstrate great potential for use as substrates in flexible reflective panel displays. However, these flexible metal substrates cannot be incorporated into the current process and equipment. Glass must be used as a carrier, which is problematic as it requires temporary lamination of metal with glass, which must be separated in a subsequent step.
Current methods for temporary lamination mostly use a high molecular gel, which due to its poor resistance to high temperature, is not suitable for laminating metal and glass. Another lamination material for metal and glass is high temperature silver gel. Coating silver gel, however, is difficult and is not cost effective. As a result, silver gel is not a satisfactory laminating material.
In addition, current methods cannot directly form a single-crystal silicon layer on a transparent substrate (such as glass), as glass is amorphous and exhibit a melting point of 600° C. If molecular beam epitaxy (MBE) is utilized to directly grow a single-crystal silicon layer, temperature must be between 700 and 800° C., or even higher. Therefore, traditional methods use anodic bonding to tightly bond a glass substrate and a single-crystal silicon substrate, followed by a polish and etching method to remove excess single-crystal silicon.
Switching elements of TFT-LCD products in the current market are mostly amorphous silicon thin film transistors (α-TFTs). For some high-end products, such as panels for digital cameras or projectors, low temperature polysilicon (LTPSS) or high temperature polysilicon (HTP) are usually adopted as switching elements. However, the electron mobility of a single-crystal silicon film is greater than 600 cm2/Vs, much greater than that of polysilicon thin film (100˜300 cm2/Vs) and amorphous silicon thin film (˜0.5 cm2/Vs). Hence, if a single-crystal silicon thin film is formed on a glass substrate, the performance of TFT elements can be greatly enhanced. In addition, related circuits can be integrated as system on panel (SOP). Glass substrates having elements formed thereon are desirable not only for applications in panel displays, but also for biochip, optic microsensors, or various integrated microelectrical products.
Hence, there is a need for a method for forming a single-crystal silicon layer on a transparent substrate.